This invention relates to improvements in a method of manufacturing gas-sealed containered food by charging a predetermined quantity of low-temperature liquefied gas through a low-temperature liquefied gas outlet into individual containers, which are still open at the top and have already a predetermined quantity of food including liquid content while the containers are successively travelling at a constant speed and then sealing each container with a lid.
By the term "containered food" is meant canned food, bottled food or the like, and by the term "gas-sealed containered food" is meant, for example, a canned food containing food (e.g., solid food plus syrup) together with a low-temperature liquefied gas.
A method of charging a predetermined quantity of a low-temperature liquefied gas is sought in various industrial fields. Particularly, a method of charging an inert low-temperature liquefied gas is desired not for packing frothable liquid food containing CO.sub.2 gas, e.g., beer, in containers but for packing non-frothable liquid food, (e.g., fruits in syrup; juice drinks; orange drinks containing orange sacs; and coffee drinks) by means of, for example, a hot filling process.
With a hot filled product in a can or the like, the can becomes depressed or convex when a negative pressure is generated as temperature of the contents falls after its sealing with a lid. Accordingly, the thickness of the can body is made sufficiently large so that it will not become depressed even when a negative pressure is generated. Recently, however in order to use cans having a thin body, it has been proposed to charge a predetermined quantity of an inert gas in the liquid state (which does not change the taste of the contents, such as liquid nitrogen) into the can containing a non-frothable drink filled while it is hot, so that pressure in the can is higher than atmospheric pressure after the can has been sealed and the content has been cooled down (at which time the liquefied gas is vaporized).
In the method of manufacturing gas-sealed containered food, in which an inert low-temperature liquefied gas (hereinafter referred to merely as low-temperature liquefied gas) is continuously charged into containers at high speed, there are problems.
In this method, a low-temperature liquefied gas is charged into containers while the containers are being moved at high speed. Therefore, the charged low-temperature liquefied gas is partly spattered to the outside of the containers and also partly vaporized to escape from the containers. Where the low-temperature liquefied gas is continuously released, it also falls into space between containers. With this method, therefore, considerable loss of low-temperature liquefied gas results. In addition, the quantity of low-temperature liquefied gas that is retained in individual containers fluctuates greatly.
To be more specific, the low-temperature liquefied gas has a very low boiling point. (For example, liquid nitrogen has a boiling point of approximately -196.degree. C., and liquid argon has a boiling point of -186.degree. C. at the atmospheric pressure.) While the low-temperature liquefied gas as released from an outlet flows toward the surface of the liquid in the container, the low-temperature liquefied gas is partly vaporized due to exposure to the surrounding atmosphere. It is also partly vaporized when it comes into contact with the liquid content. The resultant vaporized gas escapes to the outside of the container. Further, when the low-temperature liquefied gas strikes the surface of the content in the can, the low-temperature liquefied gas is partly spattered to the outside thereof by the striking impact. Still further, it is partly spattered by a blow-out action of sudden vaporization just when it reaches surface of the content. For the above reasons, a considerable amount of low-temperature liquefied gas is lost.
Moreover, the quantity of low-temperature liquefied gas (or evaporated gas) that remains in the container after the sealing thereof with a lid fluctuates greatly among individual containers.
Generally, volume of the low-temperature liquefied gas which is vaporized immediately after its release from the outlet and until it comes into contact with liquid content in the container is in proportion to the area of exposed surface of the released low-temperature liquefied gas.
From this standpoint, i.e., from the standpoint of reduction of the vaporization it has been considered to date that it is the best method to let a predetermined quantity of low-temperature liquefied gas be released from a single nozzle having a single outlet.
With this method of manufacture of gas-sealed containered food, however, a great deal of low-temperature liquefied gas is still lost, and quantity of the gas retained in the container fluctuates greatly among individual containers. Therefore, this method has not been commercially used. To overcome the above disadvantage, there has been proposed a method, in which the velocity at which the low-temperature liquefied gas reaches the content in the can, does not exceed 350 cm/sec. (as disclosed in Japanese Patent Laid-open Publication No. 161915/81).
According to this proposed method, the loss of low-temperature liquefied gas can be reduced to some extent. However, the loss is still considerable, and also the quantity of low-temperature liquefied gas (vaporized gas) retained in the container fluctuates greatly.